The FCC predicts that consumer demand for wireless bandwidth will exceed national capacity in less than two years [FCC11]. With Smartphone sales (200 million units in Q1 of 2013 [LIU13]) and their consumption of bandwidth accelerating, greater spectral efficiency is crucial. Multi-band Smartphones are projected to require up to a dozen channel filters by 2014, and rising thereafter, with the results that filter cost will soon be ˜10× that of a feature phone [KAS10,YOL12]. The prospect of ever rising cost, complexity and space requirements in Smartphones has driven the search for an ultra-wideband tunable filter. To date, research has focused on MEMS or other switched filter banks and on tunable capacitors [WU06, HIL08, MOR09, REI09, MI10], but none have met all the criteria for commercial success. Without a cost effective ultra-wideband tuning technology free of distortion, utilization of spectrum will be inadequate, adversely affecting consumers, industry and the economy.
Accordingly, there exists a need for a cost effective ultra-wideband tuning technology free of distortion, and particularly for a tunable filter employing feedforward cancellation.